I haven't tried any other games but HL1 and CS1.6 yet. Both are unplayable because the mouse driver signal seems to get screwed which causes any mouse input to be super sensitive and anything else but looking at the ground is impossible.

Switching the fusion mouse profile from default, to mac to windows doesn't change a thing. I know my problems are most likely vm related, but I wanted to ask here if anyone else has similar problems, instead of making a post at Valve's github pages.

Well HL1 and CS1.6 are also being ported to Mac natively (I checked in my OS X Steam install, and tested there too, works like a charm).So just get your native Steam install up and download it through there.Last note: It's not good to run games in a VM because VM's typically don't have really good hardware acceleration, so if, for example, your graphics card can run a game at 200FPS, well the VM will probably get somewhere between 20-60.

I'm using VMWare Workstation 9, and within VMWare Workstation I went to Edit->Preferences->Input, and for the dropdown menu labeled "Optimize mouse for games:", I changed the default setting "Automatic" to "Always". After doing this CS 1.6 started using my mouse correctly and not spazzing out looking straight down.

I also realized I needed to force hide the VMWare toolbar when fullscreen, otherwise if the mouse got to the top of the screen while playing, the toolbar would pop down which I didn't want to happen. To stop this, I just went to View->Exclusive Mode, within VMWare.

I'm using VMWare Workstation 9, and within VMWare Workstation I went to Edit->Preferences->Input, and for the dropdown menu labeled "Optimize mouse for games:", I changed the default setting "Automatic" to "Always". After doing this CS 1.6 started using my mouse correctly and not spazzing out looking straight down.

I also realized I needed to force hide the VMWare toolbar when fullscreen, otherwise if the mouse got to the top of the screen while playing, the toolbar would pop down which I didn't want to happen. To stop this, I just went to View->Exclusive Mode, within VMWare.

Hope this helps!

I haven't had the chance to try it out yet but this is very likely the solution. Thanks a lot mate!